Surface acoustic wave device including an IDT formed by a metal filled in grooves on a piezoelectric substrate

ABSTRACT

A surface acoustic wave device includes a LiNbO 3  substrate and is constructed such that the reflection coefficient of an IDT is not only high but the electromechanical coupling coefficient K 2  is also high, and the range of Euler angles of the LiNbO 3  substrate can be increased to realize a wide range of the electromechanical coupling coefficient K 2 . A plurality of grooves are provided in an upper surface of the LiNbO 3  substrate, an IDT including a plurality of electrode fingers is provided by filling a metal material in the plurality of grooves, and the metal material is Pt or W or an alloy primarily including at least one Pt or W.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a surface acoustic wave device which isused, for example, as a resonator or a band pass filter, and moreparticularly, to a surface acoustic wave device in which an IDT isformed by using a metal filled in grooves on a piezoelectric substrate.

2. Description of the Related Art

Heretofore, as a resonator and/or a band pass filter, a surface acousticwave device has been widely used. For example, in WO2006/011417A1, asurface acoustic wave device 1001 having a cross-sectional structureschematically shown in FIG. 26 has been disclosed.

In the surface acoustic wave device 1001, a plurality of grooves 1002 bare formed in an upper surface 1002 a of an LiTaO₃ substrate 1002. Ametal is filled in the plurality of grooves 1002 b, and thereby an IDT1003 including a plurality of electrode fingers made of the above metalis formed. An SiO₂ film 1004 is laminated so as to cover the uppersurface 1002 a of the LiTaO₃ substrate 1002. Since the LiTaO₃ substrate1002 has a negative temperature coefficient of frequency TCF, the SiO₂film 1004 having a positive temperature coefficient of frequency TCF islaminated to the LiTaO₃ substrate 1002, so that the absolute value ofthe temperature coefficient of frequency TCF of the surface acousticwave device 1001 can be decreased.

In addition, it is believed that since the IDT is formed by using themetal disposed in the plurality of grooves 1002 b, a high reflectioncoefficient is obtained in the IDT. In particular, when the wavelengthof a surface acoustic wave is represented by λ, and the thickness of Alfilled in the grooves 1002 b, that is, the thickness of the IDT made ofAl, is set to 0.04λ, the reflection coefficient per one electrode fingeris 0.05, and it has been shown that as the thickness of the electrode isincreased, a higher reflection coefficient can be obtained.

In addition, in Japanese Unexamined Patent Application Publication No.2004-112748, a surface acoustic wave device shown in FIG. 27 isdisclosed. In a surface acoustic wave device 1101, an IDT 1103 isprovided on a piezoelectric substrate 1102 made of LiTaO₃ or LiNbO₃. Inaddition, a protective film 1104 is arranged so as to cover the IDT1103. On the other hand, in a region other than that in which the IDT1103 and the protective film 1104 are provided, a first insulating layer1105 made of SiO₂ is provided which has a thickness equal orsubstantially equal to that of a laminated metal film of the IDT 1103and the protective film 1104 laminated to each other. In addition, asecond insulating layer 1106 made of SiO₂ is laminated so as to coverthe first insulating layer 1105. In this case, it has been shown thatsince a metal having a density greater than that of Al is used for theIDT 1103, the absolute value of the reflection coefficient can beincreased, and undesired ripples can be suppressed.

In the surface acoustic wave device 1001 disclosed in WO2006/011417A1,it has been shown that as the thickness of the IDT made of Al isincreased, the absolute value of the reflection coefficient can beincreased. However, the inventors of the present invention discoveredthat when the absolute value of the reflection coefficient is simplyincreased, superior resonant characteristics cannot be obtained. Thatis, in the surface acoustic wave device disclosed in WO2006/011417A1,although the absolute value of the reflection coefficient can beincreased by increasing the thickness of the electrode made of Al, itwas found that since the sign of the reflection coefficient is negative,many ripples are generated in a pass band, and thus, superior resonantcharacteristics cannot be obtained.

In WO2006/011417A1, for the relationship between the thickness of theIDT and the reflection coefficient, only the case in which an IDT madeof Al is used on an LiTaO₃ substrate has been described. In addition, inparagraph 0129 of WO2006/011417A1, it has been suggested that the IDTmay be formed using another metal, such as Au. However, only an IDT madeof Au has been disclosed.

In addition, according to Japanese Unexamined Patent ApplicationPublication No. 2004-112748, it has been disclosed as described abovethat when the IDT made of a metal having a density higher than that ofAl is used, the absolute value of the reflection coefficient can beincreased. However, an increase in electromechanical couplingcoefficient of a surface acoustic wave device to be obtained has notbeen particularly described.

In addition, in the structure in which the IDT is formed by filling Auin the grooves provided in the above LiNbO₃ substrate, there has been aproblem in that the range of the Euler angles of the LiNbO₃ substratewhich can be used to obtain a sufficiently high electromechanicalcoupling coefficient K² is very small.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a surfaceacoustic wave device which overcomes the problems described above, andin the surface acoustic wave device described above, an LiNbO₃ substrateis used as a piezoelectric substrate, the reflection coefficient of anIDT is not only sufficiently high but the electromechanical couplingcoefficient K² is also high, the range of the Euler angles of an LiNbO₃substrate which can be used is relatively wide, and the degree of designfreedom is increased accordingly.

According to a preferred embodiment of the present invention, a surfaceacoustic wave device includes a piezoelectric substrate including aplurality of grooves provided in an upper surface thereof and which ismade of an LiNbO₃ substrate, and an IDT including a plurality ofelectrode fingers made of a metal material which is filled in theplurality of grooves in the upper surface of the piezoelectricsubstrate, and the metal material is Pt or W or an alloy primarilyincluding at least one of Pt or W.

In the surface acoustic wave device according to this preferredembodiment of the present invention, when the wavelength of a surfaceacoustic wave is represented by λ, an electrode thickness of the IDT andθ of Euler angles (0°±10°, θ, 0°±10° of the LiNbO₃ substrate are made ofone of combinations shown in the Table 1 below. In this case, the rangeof the Euler angle of the LiNbO₃ substrate which obtains a highelectromechanical coupling coefficient K² can be further increased.

TABLE 1 ELECTRODE ELECTRODE MATERIAL THICKNESS EULER ANGLE θ Pt 0.04λ ≦Pt ≦ 0.08λ 70° ≦ θ ≦ 134° W 0.02λ ≦ W ≦ 0.04λ 70° ≦ θ ≦ 139° W 0.04λ < W≦ 0.08λ 74° ≦ θ ≦ 139°

In addition, the surface acoustic wave device preferably furtherincludes a dielectric film which is made of SiO₂ or an inorganicmaterial primarily including SiO₂ and which covers the IDT and thepiezoelectric substrate. In this case, since the temperature coefficientof frequency of the dielectric film made of SiO₂ or an inorganicmaterial primarily including SiO₂ is a positive value and thetemperature coefficient of frequency TCF of LiNbO₃ is a negative value,a surface acoustic wave device having a small overall absolute value ofthe temperature coefficient of frequency TCF can be provided.

In a surface acoustic wave device according to another preferredembodiment of the present invention, when the wavelength of a surfaceacoustic wave is represented by λ, a normalized film thickness of theIDT normalized by λ, a normalized film thickness of an SiO₂ film used asthe dielectric film normalized by λ, and θ of Euler angles (0°±10°, θ,0°±10° of the LiNbO₃ substrate are one of combinations shown in theTables 2 to 4 or Tables 5 to 7 below.

TABLE 2 RANGE OF EULER ANGLE TO SATISFY 0.2 ≧ K² LOWER UPPER LIMIT LIMITOF EULER OF EULER 4 ≦ FILM THICKNESS OF Pt ≦ 8 ANGLE θ ANGLE θ  0 ≦ FILMTHICKNESS OF SiO₂ ≦ 5 71 131  5 < FILM THICKNESS OF SiO₂ ≦ 10 71 121 10< FILM THICKNESS OF SiO₂ ≦ 15 71 117 15 < FILM THICKNESS OF SiO₂ ≦ 20 71117 20 < FILM THICKNESS OF SiO₂ ≦ 25 78 120 25 < FILM THICKNESS OF SiO₂≦ 30 78 120 30 < FILM THICKNESS OF SiO₂ ≦ 35 74 116 (The film thicknessof Pt and the film thickness of SiO₂ in the table each indicate thevalue of the normalized film thickness × 10².)

TABLE 3 RANGE OF EULER ANGLE TO SATISFY 0.2 ≧ K² LOWER LIMIT UPPER OFLIMIT OF EULER EULER 8 < FILM THICKNESS OF Pt ≦ 12 ANGLE θ ANGLE θ  0 ≦FILM THICKNESS OF SiO₂ ≦ 5 76 131  5 < FILM THICKNESS OF SiO₂ ≦ 10 77121 10 < FILM THICKNESS OF SiO₂ ≦ 15 79 117 15 < FILM THICKNESS OF SiO₂≦ 20 79 117 20 < FILM THICKNESS OF SiO₂ ≦ 25 79 123 25 < FILM THICKNESSOF SiO₂ ≦ 30 78 128 30 < FILM THICKNESS OF SiO₂ ≦ 35 77 116 (The filmthickness of Pt and the film thickness of SiO₂ in the table eachindicate the value of the normalized film thickness × 10².)

TABLE 4 RANGE OF EULER ANGLE TO SATISFY 0.2 ≧ K² LOWER LIMIT UPPER OFLIMIT OF EULER EULER 12 < FILM THICKNESS OF Pt ≦ 16 ANGLE θ ANGLE θ  0 ≦FILM THICKNESS OF SiO₂ ≦ 5 81 125  5 < FILM THICKNESS OF SiO₂ ≦ 10 85121 10 < FILM THICKNESS OF SiO₂ ≦ 15 88 119 15 < FILM THICKNESS OF SiO₂≦ 20 88 119 20 < FILM THICKNESS OF SiO₂ ≦ 25 87 121 25 < FILM THICKNESSOF SiO₂ ≦ 30 83 126 30 < FILM THICKNESS OF SiO₂ ≦ 35 78 132 (The filmthickness of Pt and the film thickness of SiO₂ in the table eachindicate the value of the normalized film thickness × 10².)

TABLE 5 RANGE OF EULER ANGLE TO SATISFY 0.2 ≧ K² LOWER LIMIT UPPER OFLIMIT OF EULER EULER 4 ≦ FILM THICKNESS OF W ≦ 8 ANGLE θ ANGLE θ  0 ≦FILM THICKNESS OF SiO₂ ≦ 5 75 133  5 < FILM THICKNESS OF SiO₂ ≦ 10 75131 10 < FILM THICKNESS OF SiO₂ ≦ 15 75 124 15 < FILM THICKNESS OF SiO₂≦ 20 82 123 20 < FILM THICKNESS OF SiO₂ ≦ 25 84 120 25 < FILM THICKNESSOF SiO₂ ≦ 30 86 116 30 < FILM THICKNESS OF SiO₂ ≦ 35 86 116 (The filmthickness of W and the film thickness of SiO₂ in the table each indicatethe value of the normalized film thickness × 10².)

TABLE 6 RANGE OF EULER ANGLE TO SATISFY 0.2 ≧ K² LOWER LIMIT UPPER OFLIMIT OF EULER EULER 8 < FILM THICKNESS OF W ≦ 12 ANGLE θ ANGLE θ  0 ≦FILM THICKNESS OF SiO₂ ≦ 5 82 133  5 < FILM THICKNESS OF SiO₂ ≦ 10 82131 10 < FILM THICKNESS OF SiO₂ ≦ 15 80 122 15 < FILM THICKNESS OF SiO₂≦ 20 86 122 20 < FILM THICKNESS OF SiO₂ ≦ 25 87 123 25 < FILM THICKNESSOF SiO₂ ≦ 30 87 122 30 < FILM THICKNESS OF SiO₂ ≦ 35 86 116 (The filmthickness of W and the film thickness of SiO₂ ≦ in the table eachindicate the value of the normalized film thickness × 10².)

TABLE 7 RANGE OF EULER ANGLE TO SATISFY 0.2 ≧ K² LOWER UPPER LIMIT OFLIMIT OF EULER EULER 12 < FILM THICKNESS OF W ≦ 16 ANGLE θ ANGLE θ  0 ≦FILM THICKNESS OF SiO₂ ≦ 5 91 128  5 < FILM THICKNESS OF SiO₂ ≦ 10 93123 10 < FILM THICKNESS OF SiO₂ ≦ 15 93 117 15 < FILM THICKNESS OF SiO₂≦ 20 85 117 20 < FILM THICKNESS OF SiO₂ ≦ 25 88 124 25 < FILM THICKNESSOF SiO₂ ≦ 30 88 126 30 < FILM THICKNESS OF SiO₂ ≦ 35 82 128 (The filmthickness of W and the film thickness of SiO₂ in the table each indicatethe value of the normalized film thickness × 10².)

As described above, when one of combinations shown in the above Tables 2to 7 is used in accordance with the type of metal material forming theIDT, the range of an Euler angle which achieves a high electromechanicalcoupling coefficient K² can be further increased.

According to various preferred embodiments of the present invention, inan IDT having a plurality of electrode fingers made of a metal materialwhich is filled in grooves in an upper surface of a LiNbO₃ substrate,since the metal material is Pt or W or an alloy primarily including atleast one of PT or W, the reflection coefficient of the IDT is not onlyhigh but a high electromechanical coupling coefficient K² can also beobtained. Furthermore, in order to provide a range of the highelectromechanical coupling coefficient K², the Euler angle of the LiNbO₃substrate can be selected from a wide range. Thus, characteristics ofthe surface acoustic wave device are improved, and furthermore, thedegree of design freedom thereof is also increased.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a partially schematic front cross-sectional view showingportions of a surface acoustic wave device according to a preferredembodiment of the present invention and FIG. 1B is a schematic plan viewof the surface acoustic wave device.

FIG. 2 is a view showing the relationship between the reflectioncoefficient and the Euler angle θ according to a preferred embodiment ofthe present invention which is obtained when Pt is used as a metalmaterial for an IDT, in which a solid line indicates results of astructure in which an SiO₂ film is laminated and a dotted line indicatesresults of a structure in which no SiO₂ film is laminated.

FIG. 3 is a view showing the relationship between the electromechanicalcoupling coefficient K² and the Euler angle θ according to a preferredembodiment of the present invention which is obtained when Pt is used asa metal material for an IDT, in which a solid line indicates results ofa structure in which an SiO₂ film is laminated and a dotted lineindicates results of a structure in which no SiO₂ film is laminated.

FIG. 4 is a view showing the relationship between the reflectioncoefficient and the Euler angle θ according to a preferred embodiment ofthe present invention which is obtained when W is used as a metalmaterial for an IDT, in which a solid line indicates results of astructure in which an SiO₂ film is laminated and a dotted line indicatesresults of a structure in which no SiO₂ film is laminated.

FIG. 5 is a view showing the relationship between the electromechanicalcoupling coefficient K² and the Euler angle θ according to a preferredembodiment of the present invention which is obtained when W is used asa metal material for an IDT, in which a solid line indicates results ofa structure in which an SiO₂ film is laminated and a dotted lineindicates results of a structure in which no SiO₂ film is laminated.

FIG. 6 is a view showing the relationship between the reflectioncoefficient and the Euler angle θ according to a related example whichis obtained when Al is used as a metal material for an IDT, in which asolid line indicates results of a structure in which an SiO₂ film islaminated and a dotted line indicates results of a structure in which noSiO₂ film is laminated.

FIG. 7 is a view showing the relationship between the electromechanicalcoupling coefficient K² and the Euler angle θ according to a relatedexample which is obtained when Al is used as a metal material for anIDT, in which a solid line indicates results of a structure in which anSiO₂ film is laminated and a dotted line indicates results of astructure in which no SiO₂ film is laminated.

FIG. 8 is a view showing the relationship between the reflectioncoefficient and the Euler angle θ according to a related example whichis obtained when Au is used as a metal material for an IDT, in which asolid line indicates results of a structure in which an SiO₂ film islaminated and a dotted line indicates results of a structure in which noSiO₂ film is laminated.

FIG. 9 is a view showing the relationship between the electromechanicalcoupling coefficient K² and the Euler angle θ according to a relatedexample which is obtained when Au is used as a metal material for anIDT, in which a solid line indicates results of a structure in which anSiO₂ film is laminated and a dotted line indicates results of astructure in which no SiO₂ film is laminated.

FIGS. 10A and 10B are views showing the relationship of the reflectioncoefficient with a normalized film thickness of a Pt film and the Eulerangle θ and the relationship of the electromechanical couplingcoefficient K² therewith, respectively, according to a preferredembodiment of the present invention, each of which is obtained when Ptis used as a metal material form an IDT and no SiO₂ film is laminated.

FIGS. 11A and 11B are views showing the relationship of the reflectioncoefficient with a normalized film thickness of a Pt film and the Eulerangle θ and the relationship of the electromechanical couplingcoefficient K² therewith, respectively, according to a preferredembodiment of the present invention, each of which is obtained when Ptis used as a metal material form an IDT and a normalized film thicknessof an SiO₂ film is about 0.05.

FIGS. 12A and 12B are views showing the relationship of the reflectioncoefficient with a normalized film thickness of a Pt film and the Eulerangle θ and the relationship of the electromechanical couplingcoefficient K² therewith, respectively, according to a preferredembodiment of the present invention, each of which is obtained when Ptis used as a metal material for an IDT and a normalized film thicknessof an SiO₂ film is about 0.1.

FIGS. 13A and 13B are views showing the relationship of the reflectioncoefficient with a normalized film thickness of a Pt film and the Eulerangle θ and the relationship of the electromechanical couplingcoefficient K² therewith, respectively, according to a preferredembodiment of the present invention, each of which is obtained when Ptis used as a metal material for an IDT and a normalized film thicknessof an SiO₂ film is about 0.15.

FIGS. 14A and 14B are views showing the relationship of the reflectioncoefficient with a normalized film thickness of a Pt film and the Eulerangle θ and the relationship of the electromechanical couplingcoefficient K² therewith, respectively, according to a preferredembodiment of the present invention, each of which is obtained when Ptis used as a metal material for an IDT and a normalized film thicknessof an SiO₂ film is about 0.2.

FIGS. 15A and 15B are views showing the relationship of the reflectioncoefficient with a normalized film thickness of a Pt film and the Eulerangle θ and the relationship of the electromechanical couplingcoefficient K² therewith, respectively, according to a preferredembodiment of the present invention, each of which is obtained when Ptis used as a metal material for an IDT and a normalized film thicknessof an SiO₂ film is about 0.25.

FIGS. 16A and 16B are views showing the relationship of the reflectioncoefficient with a normalized film thickness of a Pt film and the Eulerangle θ and the relationship of the electromechanical couplingcoefficient K² therewith, respectively, according to a preferredembodiment of the present invention, each of which is obtained when Ptis used as a metal material for an IDT and a normalized film thicknessof an SiO₂ film is about 0.3.

FIGS. 17A and 17B are views showing the relationship of the reflectioncoefficient with a normalized film thickness of a Pt film and the Eulerangle θ and the relationship of the electromechanical couplingcoefficient K² therewith, respectively, according to a preferredembodiment of the present invention, each of which is obtained when Ptis used as a metal material for an IDT and a normalized film thicknessof an SiO₂ film is about 0.35.

FIGS. 18A and 18B are views showing the relationship of the reflectioncoefficient with a normalized film thickness of a W film and the Eulerangle θ and the relationship of the electromechanical couplingcoefficient K² therewith, respectively, according to a preferredembodiment of the present invention, each of which is obtained when W isused as a metal material for an IDT and no SiO₂ film is laminated.

FIGS. 19A and 19B are views showing the relationship of the reflectioncoefficient with a normalized film thickness of a W film and the Eulerangle θ and the relationship of the electromechanical couplingcoefficient K² therewith, respectively, according to a preferredembodiment of the present invention, each of which is obtained when W isused as a metal material for an IDT and a normalized film thickness ofan SiO₂ film is about 0.05.

FIGS. 20A and 20B are views showing the relationship of the reflectioncoefficient with a normalized film thickness of a W film and the Eulerangle θ and the relationship of the electromechanical couplingcoefficient K² therewith, respectively, according to a preferredembodiment of the present invention, each of which is obtained when W isused as a metal material for an IDT and a normalized film thickness ofan SiO₂ film is about 0.1.

FIGS. 21A and 21B are views showing the relationship of the reflectioncoefficient with a normalized film thickness of a W film and the Eulerangle θ and the relationship of the electromechanical couplingcoefficient K² therewith, respectively, according to a preferredembodiment of the present invention, each of which is obtained when W isused as a metal material for an IDT and a normalized film thickness ofan SiO₂ film is about 0.15.

FIGS. 22A and 22B are views showing the relationship of the reflectioncoefficient with a normalized film thickness of a W film and the Eulerangle θ and the relationship of the electromechanical couplingcoefficient K² therewith, respectively, according to a preferredembodiment of the present invention, each of which is obtained when W isused as a metal material for an IDT and a normalized film thickness ofan SiO₂ film is about 0.2.

FIGS. 23A and 23B are views showing the relationship of the reflectioncoefficient with a normalized film thickness of a W film and the Eulerangle θ and the relationship of the electromechanical couplingcoefficient K² therewith, respectively, according to a preferredembodiment of the present invention, each of which is obtained when W isused as a metal material for an IDT and a normalized film thickness ofan SiO₂ film is about 0.25.

FIGS. 24A and 24B are views showing the relationship of the reflectioncoefficient with a normalized film thickness of a W film and the Eulerangle θ and the relationship of the electromechanical couplingcoefficient K² therewith, respectively, according to a preferredembodiment of the present invention, each of which is obtained when W isused as a metal material for an IDT and a normalized film thickness ofan SiO₂ film is about 0.3.

FIGS. 25A and 25B are views showing the relationship of the reflectioncoefficient with a normalized film thickness of a W film and the Eulerangle θ and the relationship of the electromechanical couplingcoefficient K² therewith, respectively, according to a preferredembodiment of the present invention, each of which is obtained when W isused as a metal material for an IDT and a normalized film thickness ofan SiO₂ film is about 0.35.

FIG. 26 is a schematic front cross-sectional view illustrating oneexample of a related surface acoustic wave device.

FIG. 27 is a partially cut-away front cross-sectional view illustratinganother example of a related surface acoustic wave device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, with reference to the drawings, particular preferredembodiments of the present invention will be described to provide aclear understanding of the present invention.

FIG. 1A is a partially schematic front cross-sectional view showing aportion at which an IDT of a surface acoustic wave device according to afirst preferred embodiment of the present invention is provided, andFIG. 1B is a schematic plan view of the surface acoustic wave device.

As shown in FIG. 1A, a surface acoustic wave device 1 includes an LiNbO₃substrate 2. A plurality of grooves 2 b are provided in an upper surface2 a of the LiNbO₃ substrate 2. A metal is filled in the plurality ofgrooves 2 b, so that an IDT 3 including a plurality of electrode fingersis provided. An upper surface of this IDT 3 and the upper surface 2 a ofthe LiNbO₃ substrate 2 are flush or approximately flush with each other.

An SiO₂ film 4 is preferably arranged so as to cover the upper surface 2a and the IDT 3. However, in preferred embodiments of the presentinvention, the SiO₂ film 4 may not be provided.

As shown in FIG. 1B, the surface acoustic wave device 1 preferably is aone-port type surface acoustic wave resonator which includes the IDT 3and first and second reflectors 5 and 6 disposed at both sides of theIDT 3 in a surface acoustic wave propagation direction. In addition, thereflectors 5 and 6 are grating reflectors in which both ends ofelectrode fingers are short-circuited to each other.

As in the IDT 3, the above reflectors 5 and 6 are formed by filling thesame metal as that described above in grooves provided in the uppersurface 2 a of the LiNbO₃ substrate 2. Accordingly, the reflectors 5 and6 are also flush or approximately flush with the electrode surface andthe upper surface 2 a of the LiNbO₃ substrate 2. Thus, the upper surfaceof the SiO₂ film 4 is approximately planarized over the entire surfaceacoustic wave device 1.

Although the temperature coefficient of frequency TCF of the LiNbO₃substrate 2 is a negative value, since the temperature coefficient offrequency TCF of the SiO₂ film 4 is a positive value, the absoluteoverall value of the temperature coefficient of frequency TCF isdecreased. Thus, in the surface acoustic wave device 1, the change infrequency characteristics caused by the change in temperature is small.

The surface acoustic wave device 1 of this preferred embodimentpreferably is a surface acoustic wave device which utilizes an SH wave,and the feature of this device is that the metal material for the IDT 3is preferably Pt or W or an alloy primarily including at least one of Ptor W, for example. A metal layer made of another metal material, such asan adhesion layer or a diffusion prevention layer, for example, may alsobe added to the IDT 3, or the IDT 3 may have a laminated structureincluding another metal layer.

Accordingly, in the surface acoustic wave device 1 of this preferredembodiment, the absolute value of the reflection coefficient of the IDT3 is not only increased but a high electromechanical couplingcoefficient K² can also be obtained. In addition, as shown in thefollowing experimental examples, when a surface acoustic wave device 1having a high electromechanical coupling coefficient K² is obtained, therange of the Euler angles of an LiNbO₃ substrate which can be used canbe increased. Thus, the degree of design freedom can be increased. Thiswill be described with reference to FIGS. 2 to 9.

FIGS. 6 and 7 are views showing the relationship of 8 of Euler angles(0°, θ, 0°) of an LiNbO₃ substrate with the reflection coefficient orthe electromechanical coupling coefficient K² of a surface acoustic wavedevice in which although the structure thereof is similar to that of thesurface acoustic wave device 1 of the present preferred embodiment, anIDT electrode and reflectors are made of Al, and a leakage surfaceacoustic wave is utilized.

In FIGS. 6 and 7, results are shown of the case in which a normalizedfilm thickness of the IDT 3 made of Al normalized by a wavelength λ of asurface acoustic wave is set to about 0.04 or about 0.08. In addition,the results of a structure in which an SiO₂ film 4 having a normalizedfilm thickness of about 0.25 is provided are shown by a solid line, andthe results of a structure in which no SiO₂ film 4 is provided are shownby a dotted line.

As shown in FIG. 6, it was discovered that when Al is used as anelectrode material, the reflection coefficient is not significantlyincreased.

In addition, as shown in FIG. 7, it was discovered that when the Eulerangle θ is changed, the electromechanical coupling coefficient K² can beabout 0.2 or greater. However, as shown in FIGS. 6A and 6B, when no SiO₂film 4 is provided, it was discovered that regardless of the value ofthe Euler angle θ and the film thickness of the IDT made of Al, thereflection coefficient is low, such as about 0.1 or less.

On the other hand, in FIGS. 8 and 9, the results are shown of the casein which Au having a normalized film thickness of about 0.04 or about0.08 is used as the electrode material, the normalized film thicknessbeing normalized by a wavelength λ of a surface acoustic wave. That is,the results are shown which are obtained when the IDT electrode 3 andthe reflectors 5 and 6 shown in FIG. 1 are made of Au. FIG. 8 shows therelationship between the Euler angle θ and the reflection coefficient,and FIG. 9 shows the relationship between the Euler angle θ and theelectromechanical coupling coefficient K².

In addition, also in FIGS. 8 and 9, the results are shown by a solidline which are obtained when an SiO₂ film 4 having a normalized filmthickness of about 0.25 is provided, and the results are shown by adotted line which are obtained when no SiO₂ film 4 is provided.

As shown in FIG. 8, it was discovered that as compared to the case inwhich Al is used as the electrode material shown in FIGS. 6A and 6B,when Au is used as the electrode material, the reflection coefficientcan be increased regardless of the Euler angle θ.

However, as shown in FIG. 9, in the structure in which no SiO₂ film 4 isprovided, a region having a high electromechanical coupling coefficientK², that is, a region in which the electromechanical couplingcoefficient K² is about 0.2 or greater, is in the range of about 72° toabout 131° when the film thickness of the electrode composed of Au isabout 0.04λ, and when the film thickness of the electrode made of Au isabout 0.08λ, the above region is in the range of about 85° to about119°. Thus, when the electrode thickness is changed in the range ofabout 0.04λ to about 0.08λ, it was discovered that when the Euler angleθ is not selected in the range of about 85° to about 119°, theelectromechanical coupling coefficient K² is not about 0.2 or greater.

In the structure in which the IDT 3 and the reflectors 5 and 6 are madeof Au and in which the SiO₂ film 4 is further provided, it wasdiscovered that in order to obtain an electromechanical couplingcoefficient K² of about 0.2 or greater, the Euler angle θ must be set inthe range of about 77° to about 117° when the film thickness of the Aufilm is about 0.04λ, and that when the film thickness thereof is about0.08λ, the Euler angle θ must be set in the range of about 90° to about114°. Thus, it was discovered that when the film thickness of the Aufilm is in the range of about 0.04λ to about 0.08λ, the Euler angle θmust be set in the range of about 90° to about 114°.

On the other hand, as described below, when Pt or W or an alloyprimarily composed of at least one of Pt or W is used as the metalmaterial for the IDT 3, the range of an Euler angle θ at which anelectromechanical coupling coefficient K² of about 0.2 or greater can beobtained is significantly increased. Thus, the degree of design freedomof the surface acoustic wave device can be increased.

In addition, the reason that superior characteristics can be obtainedwhen the electromechanical coupling coefficient K² is about 0.2 orgreater is that in a surface acoustic wave device used as a resonator ora band pass filter, in order to obtain a bandwidth which is required,the electromechanical coupling coefficient K² is preferablyapproximately 0.2 or greater.

FIGS. 2 and 3 are views showing the relationship of the Euler angle θ ofan LiNbO₃ substrate with the reflection coefficient or theelectromechanical coupling coefficient K² when Pt is used as the metalmaterial forming the IDT electrode 3 and the reflectors 5 and 6. InFIGS. 2 and 3, the normalized film thickness of the electrode made of Ptnormalized by a wavelength λ of a surface acoustic wave is set to about0.04 or about 0.08. In addition, as in the cases shown in FIGS. 6 to 9,in accordance with the present preferred embodiment, the resultsobtained when the SiO₂ film 4 is provided are shown by a solid line, andthe results obtained when no SiO₂ film 4 is provided are shown by adotted line.

In addition, in FIG. 3, for comparison, the results are also shown by achain line which are obtained when the IDT 3 and the reflectors 5 and 6are not provided in grooves in an upper surface of a LiNbO₃ substratebut are provided on the upper surface thereof using Pt having a filmthickness of about 0.08λ.

In addition, the normalized film thickness of the SiO₂ film 4 normalizedby a wavelength λ of a surface acoustic wave is set to about 0.25. Alsoin the following FIGS. 4 to 9, when the SiO₂ film 4 is provided, eachnormalized film thickness thereof is set to about 0.25.

As shown in FIG. 2, when Pt is used as the metal material, it wasdiscovered that compared to the case shown in FIG. 6 in which Al is usedas the electrode material, a high reflection coefficient can be obtainedwhen the electrode thickness is set to about 0.04λ or about 0.08λ.

In addition, according to the results of a comparative example shown bythe chain line, it was discovered that the electromechanical couplingcoefficient K² is low, such as about 0.2 or less, regardless of thevalue of the Euler angle θ.

On the other hand, according to the present preferred embodiment, it wasdiscovered that the range of an Euler angle at which theelectromechanical coupling coefficient K² is increased to about 0.2 orgreater is increased. That is, when no SiO₂ film 4 is provided, it wasdiscovered that when the electrode thickness of Pt is about 0.04λ, therange of θ at which the electromechanical coupling coefficient K² isabout 0.2 or greater is about 70° to about 135°, and that when theelectrode thickness of Pt is about 0.08λ, the above range is about 70°to about 134°. Thus, it was discovered that when the electrode thicknessof Pt is in the range of about 0.04λ to about 0.08λ, the Euler angle θmay be set in the range of about 70° to about 134°. Accordingly,compared to the case in which Au is used as the metal material, therange of the Euler angle θ can be significantly increased by using Pt.

In addition, when the SiO₂ film 4 is provided, it was discovered fromFIG. 3 that when the electrode thickness of the Pt film is about 0.04λ,a region in which the electromechanical coupling coefficient K² is about0.2 or greater is in the range of an Euler angle θ of about 76° to about120°, and that when the electrode thickness is about 0.08λ, the regionis in the range of about 78° to about 128°. Thus, it was discovered thatwhen the electrode thickness is in the range of about 0.04λ to about0.08λ, the Euler angle θ may be set in the range of about 78° to about120°.

Accordingly, in the structure in which the SiO₂ film 4 is provided, itwas discovered that compared to the case in which the Au film is used,the range of the Euler angle θ can be significantly increased by usingthe Pt film.

FIGS. 4 and 5 are views showing the relationship of the Euler angle θwith the reflection coefficient or the electromechanical couplingcoefficient K². In FIGS. 4 and 5, the normalized film thickness of Wused as the metal material for the IDT 3 and the reflectors 5 and 6 isset to about 0.02, about 0.04 or about 0.08. Furthermore, in FIGS. 4 and5, the results obtained when the SiO₂ film 4 is provided are shown by asolid line, and the results obtained when no SiO₂ film 4 is provided areshown by a dotted line.

As shown in FIG. 4, as in the case in which W is used as the metalmaterial, it was discovered that compared to the case in which Al isused, a high reflection coefficient can be obtained regardless of therange of the Euler angle θ.

In addition, as shown in FIG. 5, in the structure in which no SiO₂ film4 is provided, it was discovered that the range of an Euler angle whichcan achieve an electromechanical coupling coefficient K² of about 0.2 ormore may be set to about 70° to about 144° when the film thickness ofthe W film is about 0.02λ, that the range may be set to about 70° toabout 139° when the film thickness is about 0.04λ, and that the rangemay be set to about 74° to about 139° when the film thickness is about0.08λ. Accordingly, when W is used as the metal material, it wasdiscovered that when the film thickness thereof is in the range of about0.02λ to about 0.04λ, the Euler angle θ may be set in the range of about70° to about 139°, and that when the film thickness is in the range ofabout 0.04λ to about 0.08λ, the Euler angle θ may be set in the range ofabout 74° to about 139°. Thus, compared to the range of about 85° toabout 119° obtained when Au is used, the range of the Euler angle θ canbe significantly increased. In the structure in which the SiO₂ film 4 isprovided, it was discovered from FIG. 5 that when the electrodethickness of W is about 0.02λ, the range of an Euler angle θ which canincrease the electromechanical coupling coefficient K² to about 0.2 orgreater may be set to about 87° to about 119°, that when the electrodethickness is about 0.04λ, the above range may be set to about 84° toabout 120°, and that when the electrode thickness is about 0.08λ, theabove range may be set to about 82° to about 123°. That is, it wasdiscovered that when the electrode thickness of W is in the range ofabout 0.02, to about 0.04λ, the Euler angle θ may be set in the range ofabout 87° to about 119°, and that when the electrode thickness of W isin the range of about 0.04λ to about 0.08λ, the Euler angle θ may be setin the range of about 84° to about 120°. Accordingly, it was discoveredthat compared to the range of about 90° to about 114° obtained when theAu film is used, the range of the Euler angle θ can be significantlyincreased.

When the results described with reference to FIGS. 2 to 9 aresummarized, a combination among the metal material used for anelectrode, the electrode thickness of the above metal material, and theEuler angle θ, which achieves an electromechanical coupling coefficientK² of about 0.2 or greater, corresponds to one of combinations shown inTable 8 below. Table 8 shows the results of the structure in which noSiO₂ film is laminated.

TABLE 8 ELECTRODE ELECTRODE EULER MATERIAL THICKNESS ANGLE θ Pt 0.04λ ≦Pt ≦ 0.08λ 70° ≦ θ ≦ 134° W 0.02λ ≦ W ≦ 0.04λ 70° ≦ θ ≦ 139° W 0.04λ < W≦ 0.08λ 74° ≦ θ ≦ 139° Au 0.04λ ≦ Au ≦ 0.08λ 85° ≦ θ ≦ 119°

In Table 8, for comparison, the case in which Au is used as the metalmaterial is also shown.

In Table 8, when no SiO₂ film is provided, the range of the electrodethickness and the range of the Euler angle θ in which theelectromechanical coupling coefficient K² is about 0.2 or greater areshown for each electrode material.

In the structure in which the SiO₂ film is provided as a dielectric filmto cover the IDT electrode, the inventors of the present invention alsotook the normalized film thickness of the SiO₂ film into considerationin addition to the electrode material and the electrode thickness, andthe range of an Euler angle θ at which the electromechanical couplingcoefficient K² is about 0.2 or greater was investigated. The resultswill be described below for each metal material.

FIGS. 10A and 10B to FIGS. 17A and 17B are views showing therelationship of the reflection coefficient with the Euler angle θ andthe relationship of the electromechanical coupling coefficient K²therewith, respectively, each of which is obtained when Pt is used asthe metal material and SiO₂ films having various film thicknesses areprovided.

In addition, FIGS. 10A and 10B show the results obtained when thenormalized film thickness of the SiO₂ film normalized by λ is 0, thatis, when no SiO₂ film is provided, and FIGS. 11A to 17B show the resultsobtained when the normalized film thickness of the SiO₂ film is about0.05, about 0.1, about 0.15, about 0.2, about 0.25, about 0.3, or about0.35. In addition, the film of Pt used as the metal material forming theIDT 3 and the reflectors 5 and 6 is formed to have various normalizedfilm thicknesses as shown in FIGS. 10A to 17B. As shown in FIG. 2described above, when Pt is used as the metal material, compared to thecase in which Al is used, a high reflection coefficient can be obtainedregardless of the range of the Euler angle θ. In FIG. 10A to FIG. 17A,it was also discovered that even when the film thickness of the Pt filmis variously changed, a high reflection coefficient can be obtainedregardless of the value of the Euler angle θ.

On the other hand, as apparent from FIG. 10B to FIG. 17B, it discoveredthat when the normalized film thickness of Pt is in the range of about0.04 to about 0.08, if the range of the normalized film thickness of theSiO₂ film and the range of the Euler angle θ correspond to one ofcombinations shown in Table 9 below, the electromechanical couplingcoefficient K² can be made about 0.2 or greater. In addition, in Table9, the lower limit and the upper limit of the range of the Euler angle θare shown. For example, Table 9 indicates that when the film thicknessof the SiO₂ film is about 0.05 or less, the Euler angle θ may be set inthe range of about 71° to about 131°.

In addition, when the normalized film thickness of the Pt film is in therange of more than about 0.08 to about 0.12, the range of the filmthickness of the SiO₂ film and the range of the Euler angle θ may bemade to correspond to one of combinations shown in Table 10 below, andwhen the normalized film thickness of the Pt film is in the range ofabout 0.12 to about 0.16, the range of the film thickness of the SiO₂film and the range of the Euler angle θ may correspond to one ofcombinations shown in Table 11 below, so that the electromechanicalcoupling coefficient K² is about 0.2 or greater as in the case describedabove. Tables 9 to 11 are based on the results shown in FIGS. 10A to 17Bdescribed above.

TABLE 9 RANGE OF EULER ANGLE TO SATISFY 0.2 ≧ K² LOWER UPPER LIMIT OFLIMIT OF EULER EULER 4 ≦ FILM THICKNESS OF Pt ≦ 8 ANGLE θ ANGLE θ  0 ≦FILM THICKNESS OF SiO₂ ≦ 5 71 131  5 < FILM THICKNESS OF SiO₂ ≦ 10 71121 10 < FILM THICKNESS OF SiO₂ ≦ 15 71 117 15 < FILM THICKNESS OF SiO₂≦ 20 71 117 20 < FILM THICKNESS OF SiO₂ ≦ 25 78 120 25 < FILM THICKNESSOF SiO₂ ≦ 30 78 120 30 < FILM THICKNESS OF SiO₂ ≦ 35 74 116 (The filmthickness of Pt and the film thickness of SiO₂ in the table eachindicate the value of the normalized film thickness × 10².)

TABLE 10 RANGE OF EULER ANGLE TO SATISFY 0.2 ≧ K² LOWER UPPER LIMIT OFLIMIT OF EULER EULER 8 < FILM THICKNESS OF Pt ≦ 12 ANGLE θ ANGLE θ  0 ≦FILM THICKNESS OF SiO₂ ≦ 5 76 131  5 < FILM THICKNESS OF SiO₂ ≦ 10 77121 10 < FILM THICKNESS OF SiO₂ ≦ 15 79 117 15 < FILM THICKNESS OF SiO₂≦ 20 79 117 20 < FILM THICKNESS OF SiO₂ ≦ 25 79 123 25 < FILM THICKNESSOF SiO₂ ≦ 30 78 128 30 < FILM THICKNESS OF SiO₂ ≦ 35 77 116 (The filmthickness of Pt and the film thickness of SiO₂ in the table eachindicate the value of the normalized film thickness × 10².)

TABLE 11 RANGE OF EULER ANGLE TO SATISFY 0.2 ≧ K² LOWER UPPER LIMIT OFLIMIT OF EULER EULER 12 < FILM THICKNESS OF Pt ≦ 16 ANGLE θ ANGLE θ  0 ≦FILM THICKNESS OF SiO₂ ≦ 5 81 125  5 < FILM THICKNESS OF SiO₂ ≦ 10 85121 10 < FILM THICKNESS OF SiO₂ ≦ 15 88 119 15 < FILM THICKNESS OF SiO₂≦ 20 88 119 20 < FILM THICKNESS OF SiO₂ ≦ 25 87 121 25 < FILM THICKNESSOF SiO₂ ≦ 30 83 126 30 < FILM THICKNESS OF SiO₂ ≦ 35 78 132 (The filmthickness of Pt and the film thickness of SiO₂ in the table eachindicate the value of the normalized film thickness × 10².)

FIGS. 18A and 18B to FIGS. 25A and 25B are views showing therelationship of the reflection coefficient with the Euler angle θ andthe relationship of the electromechanical coupling coefficient K²therewith, respectively, each of which is obtained when W is used as themetal material and SiO₂ films having various film thicknesses areprovided.

In addition, FIGS. 18A and 18B show the results obtained when thenormalized film thickness of the SiO₂ film normalized by λ is 0, thatis, when no SiO₂ film is provided, and FIGS. 19A to 25B show the resultsobtained when the normalized film thickness of the SiO₂ film is about0.05, about 0.1, about 0.15, about 0.2, about 0.25, about 0.3, or about0.35. In addition, the film of W used as the metal material for the IDT3 and the reflectors 5 and 6 is configured to have various normalizedfilm thicknesses as shown in FIGS. 18A to 25B. As shown in FIG. 4described above, when W is used as the metal material, compared to thecase in which Al is used, a high reflection coefficient can be obtainedregardless of the range of the Euler angle θ. In FIG. 18A to FIG. 25A,it was also discovered that even when the film thickness of the W filmis variously changed, a high reflection coefficient can be obtainedregardless of the value of the Euler angle θ.

On the other hand, as shown in FIG. 18B to FIG. 25B, it was discoveredthat when the normalized film thickness of W is in the range of about0.04 to about 0.08, if the range of the normalized film thickness of theSiO₂ film and the range of the Euler angle θ correspond to one ofcombinations shown in Table 12 below, the electromechanical couplingcoefficient K² is about 0.2 or greater. In addition, in Table 12, thelower limit and the upper limit of the range of the Euler angle θ areshown. For example, Table 12 indicates that when the film thickness ofthe SiO₂ film is about 0.05 or less, the Euler angle θ may be set in therange of about 75° to about 133°.

In addition, when the film thickness of the W film is in the range ofabout 0.08 to about 0.12, the range of the film thickness of the SiO₂film and the range of the Euler angle θ may correspond to one ofcombinations shown in Table 13 below, and when the normalized filmthickness of the W film is in the range of about 0.12 to about 0.16, therange of the film thickness of the SiO₂ film and the range of the Eulerangle θ may correspond to one of combinations shown in Table 14 below,so that the electromechanical coupling coefficient K² is about 0.2 orgreater as in the case described above. Tables 12 to 14 are based on theresults shown in FIGS. 18A to 25B described above.

TABLE 12 RANGE OF EULER ANGLE TO SATISFY 0.2 ≧ K² LOWER UPPER LIMIT OFLIMIT OF EULER EULER 4 ≦ FILM THICKNESS OF W ≦ 8 ANGLE θ ANGLE θ  0 ≦FILM THICKNESS OF SiO₂ ≦ 5 75 133  5 < FILM THICKNESS OF SiO₂ ≦ 10 75131 10 < FILM THICKNESS OF SiO₂ ≦ 15 75 124 15 < FILM THICKNESS OF SiO₂≦ 20 82 123 20 < FILM THICKNESS OF SiO₂ ≦ 25 84 120 25 < FILM THICKNESSOF SiO₂ ≦ 30 86 116 30 < FILM THICKNESS OF SiO₂ ≦ 35 86 116 (The filmthickness of W and the film thickness of SiO₂ in the table each indicatethe value of the normalized film thickness × 10².)

TABLE 13 RANGE OF EULER ANGLE TO SATISFY 0.2 ≧ K² LOWER UPPER LIMIT OFLIMIT OF EULER EULER 8 < FILM THICKNESS OF W ≦ 12 ANGLE θ ANGLE θ  0 ≦FILM THICKNESS OF SiO₂ ≦ 5 82 133  5 < FILM THICKNESS OF SiO₂ ≦ 10 82131 10 < FILM THICKNESS OF SiO₂ ≦ 15 80 122 15 < FILM THICKNESS OF SiO₂≦ 20 86 122 20 < FILM THICKNESS OF SiO₂ ≦ 25 87 123 25 < FILM THICKNESSOF SiO₂ ≦ 30 87 122 30 < FILM THICKNESS OF SiO₂ ≦ 35 86 116 (The filmthickness of W and the film thickness of SiO₂ in the table each indicatethe value of the normalized film thickness × 10².)

TABLE 14 RANGE OF EULER ANGLE TO SATISFY 0.2 ≧ K² LOWER UPPER LIMIT OFLIMIT OF EULER EULER 12 < FILM THICKNESS OF W ≦ 16 ANGLE θ ANGLE θ  0 ≦FILM THICKNESS OF SiO₂ ≦ 5 91 128  5 < FILM THICKNESS OF SiO₂ ≦ 10 93123 10 < FILM THICKNESS OF SiO₂ ≦ 15 93 117 15 < FILM THICKNESS OF SiO₂≦ 20 85 117 20 < FILM THICKNESS OF SiO₂ ≦ 25 88 124 25 < FILM THICKNESSOF SiO₂ ≦ 30 88 126 30 < FILM THICKNESS OF SiO₂ ≦ 35 82 128 (The filmthickness of W and the film thickness of SiO₂ in the table each indicatethe value of the normalized film thickness × 10².)

As described above, when the IDT electrode is formed, the metal materialis filled in the grooves provided in the upper surface of the LiNbO₃substrate. In this case, in addition to the metals described above, themetal material may be an alloy primarily including at least one of Pt orW.

In addition, in the above-described experimental examples, although theSiO₂ film was preferably provided, instead of the SiO₂ film, adielectric film made of an inorganic material primarily including anSiO₂ film, for example, may also be used. In both cases, since having apositive temperature coefficient of frequency, when the dielectric filmsdescribed above are each used in combination with an LiNbO₃ substratehaving a negative temperature coefficient of frequency, the absolutevalue of the temperature coefficient of frequency of the surfaceacoustic wave device can be decreased. That is, a surface acoustic wavedevice having superior temperature characteristics can be provided.

In addition, the electrode structure of the surface acoustic wave deviceformed according to preferred embodiments of the present invention isnot limited to that shown in FIG. 1, and preferred embodiments of thepresent invention may be applied, for example, to surface acoustic waveresonators and surface acoustic wave filters which have variouselectrode structures.

In addition, according to preferred embodiments of the presentinvention, it has been shown as described above that the Euler angles(φ, θ, ψ) of LiNbO₃ are not particularly limited. However, when aRayleigh wave or an SH wave is utilized as a surface acoustic wave, theEuler angle φ is preferably in the range of about 0°±10°, the Eulerangle θ is preferably in the range of about 70° to about 180°, and theEuler angle ψ is preferably in the range of about 0°±10°, for example.That is, when the Euler angles are set in the range of (0°±10°, 70° to180°, 0°±10°), the Rayleigh wave and the SH wave can be preferablyutilized. More particular, in the range of (0°±10°, 90° to 180°,0°±10°), the SH wave can be more preferably utilized.

In addition, an LSAW wave may also be utilized, and in this case, theEuler angles may preferably be set in the range of (0°±10°, 110° to160°, 0°±10°. In addition, in the preferred embodiments of the presentinvention, although the electrode structure of a one-port type SAWresonator is shown, the surface acoustic wave device of preferredembodiments of the present invention can be widely applied to otherresonator structures or other resonator type surface acoustic wavefilters.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A surface acoustic wave device comprising: a piezoelectric substrateincluding a plurality of grooves provided in an upper surface thereofand being made of an LiNbO₃ substrate; and an IDT including a pluralityof electrode fingers made of a metal material which is filled in theplurality of grooves in the upper surface of the piezoelectricsubstrate; wherein the metal material is Pt or W or an alloy primarilyincluding at least one of Pt or W; and when a wavelength of a surfaceacoustic wave is represented by λ, an electrode thickness of the IDT andθ of Euler angles (0°±10°, θ, 0°±10°) of the LiNbO₃ substrate are one ofcombinations shown in Table 1: TABLE 1 ELECTRODE ELECTRODE EULERMATERIAL THICKNESS ANGLE θ Pt 0.04λ ≦ Pt ≦ 0.08λ 70° ≦ θ ≦ 134° W 0.02λ≦ W ≦ 0.04λ 70° ≦ θ ≦ 139° W 0.04λ < W ≦ 0.08λ 74° ≦ θ ≦ 139°.


2. The surface acoustic wave device according to claim 1, furthercomprising a dielectric film made of SiO₂ or an inorganic materialprimarily including SiO₂ and arranged to cover the IDT and thepiezoelectric substrate.
 3. A surface acoustic wave device comprising: apiezoelectric substrate including a plurality of grooves provided in anupper surface thereof and being made of an LiNbO₃ substrate; an IDTincluding a plurality of electrode fingers made of a metal materialwhich is filled in the plurality of grooves in the upper surface of thepiezoelectric substrate; and a dielectric film made of SiO₂ or aninorganic material primarily including SiO₂ and arranged to cover theIDT and the piezoelectric substrate; wherein the metal material is Pt orW or an alloy primarily including at least one of Pt or W; and when awavelength of a surface acoustic wave is represented by λ, a normalizedfilm thickness of the IDT normalized by λ, a normalized film thicknessof an SiO₂ film used as the dielectric film normalized by λ, and θ ofEuler angles (0°±10°, θ, 0°±10°) of the LiNbO₃ substrate are one ofcombinations shown in Tables 2 to 7: TABLE 2 RANGE OF EULER ANGLE TOSATISFY 0.2 ≧ K² LOWER UPPER LIMIT OF LIMIT OF EULER EULER 4 ≦ FILMTHICKNESS OF Pt ≦ 8 ANGLE θ ANGLE θ  0 ≦ FILM THICKNESS OF SiO₂ ≦ 5 71131  5 < FILM THICKNESS OF SiO₂ ≦ 10 71 121 10 < FILM THICKNESS OF SiO₂≦ 15 71 117 15 < FILM THICKNESS OF SiO₂ ≦ 20 71 117 20 < FILM THICKNESSOF SiO₂ ≦ 25 78 120 25 < FILM THICKNESS OF SiO₂ ≦ 30 78 120 30 < FILMTHICKNESS OF SiO₂ ≦ 35 74 116 (the film thickness of Pt and the filmthickness of SiO₂ in the table each indicate the value of the normalizedfilm thickness × 10²)

TABLE 3 RANGE OF EULER ANGLE TO SATISFY 0.2 ≧ K² LOWER UPPER LIMIT OFLIMIT OF EULER EULER 8 < FILM THICKNESS OF Pt ≦ 12 ANGLE θ ANGLE θ  0 ≦FILM THICKNESS OF SiO₂ ≦ 5 76 131  5 < FILM THICKNESS OF SiO₂ ≦ 10 77121 10 < FILM THICKNESS OF SiO₂ ≦ 15 79 117 15 < FILM THICKNESS OF SiO₂≦ 20 79 117 20 < FILM THICKNESS OF SiO₂ ≦ 25 79 123 25 < FILM THICKNESSOF SiO₂ ≦ 30 78 128 30 < FILM THICKNESS OF SiO₂ ≦ 35 77 116 (the filmthickness of Pt and the film thickness of SiO₂ in the table eachindicate the value of the normalized film thickness × 10²)

TABLE 4 RANGE OF EULER ANGLE TO SATISFY 0.2 ≧ K² LOWER UPPER LIMIT OFLIMIT OF EULER EULER 12 < FILM THICKNESS OF Pt ≦ 16 ANGLE θ ANGLE θ  0 ≦FILM THICKNESS OF SiO₂ ≦ 5 81 125  5 < FILM THICKNESS OF SiO₂ ≦ 10 85121 10 < FILM THICKNESS OF SiO₂ ≦ 15 88 119 15 < FILM THICKNESS OF SiO₂≦ 20 88 119 20 < FILM THICKNESS OF SiO₂ ≦ 25 87 121 25 < FILM THICKNESSOF SiO₂ ≦ 30 83 126 30 < FILM THICKNESS OF SiO₂ ≦ 35 78 132 (the filmthickness of Pt and the film thickness of SiO₂ in the table eachindicate the value of the normalized film thickness × 10²)

TABLE 5 RANGE OF EULER ANGLE TO SATISFY 0.2 ≧ K² LOWER UPPER LIMIT OFLIMIT OF EULER EULER 4 ≦ FILM THICKNESS OF W ≦ 8 ANGLE θ ANGLE θ  0 ≦FILM THICKNESS OF SiO₂ ≦ 5 75 133  5 < FILM THICKNESS OF SiO₂ ≦ 10 75131 10 < FILM THICKNESS OF SiO₂ ≦ 15 75 124 15 < FILM THICKNESS OF SiO₂≦ 20 82 123 20 < FILM THICKNESS OF SiO₂ ≦ 25 84 120 25 < FILM THICKNESSOF SiO₂ ≦ 30 86 116 30 < FILM THICKNESS OF SiO₂ ≦ 35 86 116 (the filmthickness of W and the film thickness of SiO₂ in the table each indicatethe value of the normalized film thickness × 10²)

TABLE 6 RANGE OF EULER ANGLE TO SATISFY 0.2 ≧ K² LOWER UPPER LIMIT OFLIMIT OF EULER EULER 8 < FILM THICKNESS OF W ≦ 12 ANGLE θ ANGLE θ  0 ≦FILM THICKNESS OF SiO₂ ≦ 5 82 133  5 < FILM THICKNESS OF SiO₂ ≦ 10 82131 10 < FILM THICKNESS OF SiO₂ ≦ 15 80 122 15 < FILM THICKNESS OF SiO₂≦ 20 86 122 20 < FILM THICKNESS OF SiO₂ ≦ 25 87 123 25 < FILM THICKNESSOF SiO₂ ≦ 30 87 122 30 < FILM THICKNESS OF SiO₂ ≦ 35 86 116 (the filmthickness of W and the film thickness of SiO₂ in the table each indicatethe value of the normalized film thickness × 10²)

TABLE 7 RANGE OF EULER ANGLE TO SATISFY 0.2 ≧ K² LOWER UPPER LIMIT OFLIMIT OF EULER EULER 12 < FILM THICKNESS OF W ≦ 16 ANGLE θ ANGLE θ  0 ≦FILM THICKNESS OF SiO₂ ≦ 5 91 128  5 < FILM THICKNESS OF SiO₂ ≦ 10 93123 10 < FILM THICKNESS OF SiO₂ ≦ 15 93 117 15 < FILM THICKNESS OF SiO₂≦ 20 85 117 20 < FILM THICKNESS OF SiO₂ ≦ 25 88 124 25 < FILM THICKNESSOF SiO₂ ≦ 30 88 126 30 < FILM THICKNESS OF SiO₂ ≦ 35 82 128 (the filmthickness of W and the film thickness of SiO₂ in the table each indicatethe value of the normalized film thickness × 10²).